Conventional feeding bottles comprise a container and a teat held on the container by a screw-on collar. A problem with conventional feeding bottles is that as an infant sucks on the teat a negative pressure builds up within the container as a result of which it becomes progressively more difficult to feed which can give rise to problems such as colic.
Various solutions have been proposed for alleviating the problem for example providing valves allowing air ingress. One example of such a solution is described in European patent application EP0845971. According to this document a feeding bottle includes a reservoir tube communicating at its upper end with a vent to atmosphere. The reservoir tube has a bulbous upper reservoir portion with an air tube projecting down into it from the air vent. An air conduit portion projects down from the reservoir portion to a point close to the bottom of the container. In the upright position the container is filled with liquid nearly to the height of the reservoir portion. When the container is inverted the end of the air conduit portion projects above the level of the liquid and the liquid previously in the air conduit portion drains into the reservoir portion and sits below the end of the air tube. As a result an air passage is provided from the vent via the air tube into the reservoir portion and through the air conduit to the bottle such that pressure equalisation is provided when the infant drinks. However, there are various disadvantages to this arrangement. Firstly a very complex arrangement is required. Furthermore because no valves are provided, if the infant distorts the teat while feeding for example by biting down on it there is less resistance and liquid is pushed away from the teat.
Another approach is described in U.S. Pat. No. 6,499,615 which describes a bottle having an angled neck and a valved vent tube. Once again complex and specialised components are required for this arrangement which also presents cleaning difficulties and even choking hazards as a result of the numerous small parts involved.
Furthermore, in known valved, vented feeding bottles, during the bottle feeding process the pressures fluctuate between positive and negative throughout the feed. When the infant bites down on or compresses the teat during feeding this action creates positive pressure in the bottle as the milk is pushed back into the bottle, acting on the valve to close it and directing milk flow out of the teat. As the infant creates suction to draw more milk from the bottle a negative pressure is induced in the bottle as milk is dispensed and when this occurs the valve at the end of the tube opens allowing air into the bottle. However in known systems a relatively significant negative pressure is required before the valve opens to allow air to vent such that the infant must suck unnaturally hard before pressure equalisation takes place. Accordingly known systems do not closely mimic natural feeding.